With the advancement in technology, communications systems are capable of providing better services to the users. In some applications that make use of presence services, communication devices report (“publish”) to a central network entity (a “presence server”) status or presence information of users of the communication devices (“presentities”). The presence server distributes (“notifies”) the presence information to other users (“watchers”) in the communications system. Generally, the presence information includes information such as the status of the communication device, availability of a user of the device, location of the communication device, current operation being performed by the device, preferred communications of the user, and the like.
Standard presence functionality allows a watcher (user, device, or application) to subscribe to the presence server to receive presence information related to one or more presentities. The subscription can be done individually for the one or more presentities or by using a Presence Resource List that includes multiple presentities. Upon subscribing to the one or more specified presentities, the watcher is notified of presence information for the specified presentites.
Internet Engineering Task Force (IETF) Request for Comments (RFCs) 4460 and 4461 discuss an Extensible Markup Language (XML) based method that allows SIP/SIMPLE watchers to supply notification filter criteria as part of the subscription. The presence server then evaluates the criteria to determine if and when to notify the subscribing watcher. However, RFCs 4460 and 4461 allow a watcher to reference (in the supplied notification criteria) only an unordered plurality of synchronous current presence values that occur at the same time. For example, the criteria can comprise that the watcher be notified when a presence information element A has a value of ‘a1’, and a presence information element B has a value of ‘b1’ at the same time. This simple subscription and notification mechanism is generally sufficient for consumer users. However, it is insufficient to meet the needs of certain other users such as public safety users who would benefit from more sophisticated techniques that include, for example, the ability to specify notification triggers based on: historical and future values of presence information elements; an ordered or unordered sequence of events; and/or time period parameters for events corresponding to changes to presence information, which is not available in known subscription and notification mechanisms.
Accordingly, there is a need for a method for presence notification based on a sequence of events.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.